Implantable cardiac stimulation devices are well known in the art. They include implantable pacemakers, which provide stimulation pulses to a heart to cause a heart, which would normally or otherwise beat too slowly or at an irregular rate, to beat at a controlled normal rate. They also include defibrillators, which detect when the atria and/or the ventricles of the heart are in fibrillation and apply cardioverting or defibrillating electrical energy to the heart to restore the heart to a normal rhythm. Implantable cardiac stimulation devices may also include the combined functionalities of a pacemaker and a defibrillator.
Implantable cardiac stimulation devices have become extremely sophisticated. As is well known, they are able to provide therapy to a heart based upon numerous different programmable parameters. Such programmable parameters may, for example, control therapy modality, pacing rates, refractory periods, pacing and defibrillating pulse energies, detection sensitivities, and the like.
Programmable parameter selection is normally achieved with an external programmer, which establishes a communication channel via telemetry with the implanted device. To that end, the implantable devices include a telemetry circuit including a transmitter for transmitting device related information and electrograms to the external programmer and a receiver for receiving information, such as programmable parameter commands, from the external programmer. As a result of such external programmability, the implanted devices may be reprogrammed by the physician to continually adapt the device to a patient's changing condition.
More recently, with improvements in increased memory storage capacity, the implantable cardiac storage devices are now also seen as being capable of storing cardiac data which could not be previously stored. Such data may include, for example, device history data, cardiac data including stored electrograms to be used at follow-up visits, or cardiac data useful in diagnosing cardiac conditions other than those currently being treated by the implanted device.
As can thus be seen, the telemetry channel may be used to both read data from the implanted device and to send data into the device. Some of the data that is sent into the device is information that is passive and simply recorded in memory, to be read back at a later time. Other data that is sent into the device is active and causes changes in the behavior or operation of the device. Some of the active data, when sent to the device, will cause operational changes, which do not impact the therapy provided to the patient. Such data may include diagnostic data recording modes or real time data transmission channel selections. Active data sent to the implanted device does impact on the therapy received by the patient. Such data may include parameters such as pacing rate, mode, and rate responsive slope, for example. In some other cases, reading of data from an implanted device can cause active changes in the therapy being delivered to the patient. For example, temporary changes in pacing rate and modality may be required for reading measured data while more permanent changes are also possible results of reading data from a device.
Hence, there are a number of potential uses for the telemetry interface which can benefit from the ability to read data from an implanted device and to control active behavior of the device without affecting the therapy delivered to the patient. To ensure that the health and safety of the patient are maintained at all times, it is particularly desirable, if not necessary, to require that the possibility of affecting the therapy delivered be reduced to effectively zero. Examples of applications that could utilize this function are transtelephonic monitoring devices, patient activated data recording device, Holter-style recording instruments, stand-alone patient monitoring devices, or patient monitoring devices linked to a central station.
Unfortunately, these applications cannot use the same RF telemetry communications protocol as is typically used by programmers to communicate with and control the implanted device. This is because the potential exists for inadvertently affecting the therapy delivered by the device when errors enter the communications link, either as noise or interference in the RF link or by errors in the operation of the non-programming monitoring devices.
Prior systems have failed to provide adequate security to permit partial programming or non-programming devices to communicate with an implantable device. For example, systems are known wherein partial programming or non-programming external devices communicate with implanted devices using the same protocol as the devices full-featured programmer. These systems simply rely on the partial programming or non-programming device having limited or no programming ability. However, because they use the same protocol as the devices programmer, noise or interference with the communication link could cause the programmable parameters of the implanted device and thus the therapy delivered by the implanted device to be inadvertently affected by communication with a partial programming or non-programming device.
Other systems fail to recognize that partial programming or non-programming devices may be in communication with an implanted device. For example, U.S. Pat. No. 4,875,483 describes a system wherein an implantable stimulator uses a program access code to control who may change the programming of the device. Identification of an external device type by an implantable device is not contemplated.
U.S. Pat. No. 5,725,559 describes a system wherein an implantable stimulator uses codes to determine the current programming of the implanted device and the level of therapy the device is authorized to provide. While the system permits some level of personnel to provide maintenance type work on the device using the programmer, only a physician can upgrade the therapies given to the patient. However, the concept of the implanted device communicating with different types of external devices other than a programmer is not addressed.
U.S. Pat. No. 5,843,138 describes a system wherein a programmer is capable of programming the implanted device in a conventional way and also downloading new control software to the implanted device, subject to predetermined system conditions. Upon interrogating the implanted device, the programmer determines whether the device is of the type, which it is able to modify. Again, the described implanted device fails to respond to the need of being capable of different types of external devices and identifying the type of external device with which it is communicating for the purpose of providing an appropriate response.
Therefore, there is a need in the art for a new and improved implantable cardiac stimulation device which may communicate with various types of external devices including programmers which may change the operation of the implantable device and other external devices such as monitors which are intended to make minor modifications in the device operation and/or read data from the implanted device. More particularly, there is a need in the art for an implantable cardiac stimulation device which is capable of communicating with a plurality of different external devices, detecting the type of external device in which it is communicating, and then providing a suitable appropriate response to the external device.